Dendritic macromolecules represent a new type of polymeric architecture, which has become popular in a variety of studies, including application level, in the last two decades. The branches-upon-branches is an unique architectural feature of these macromolecules and they enjoy being the most monodispersed of all synthetic macromolecules.
The systematic studies of the dendritic macromolecules may be traced back first to the series of the so-called poly (amido amine) or Starburst dendrimers, pioneered by Tomalia and co-workers, Polym. J. (Tokyo), 117 (1985), U.S. Pat. No. 4,507,466; U.S. Pat. No. 4,558,320 and U.S. Pat. No. 4,737,550. These dendrimers possess primarily an amide as the linkage unit and a tertiary amine as the branch point. Another popular dendritic macromolecular series is the poly (propylene imine) dendrimers, advanced by Meijer and de Brabander-van den Berg, Angew. Chem. Int. Ed. Engl. 1308 (1993), WO 93/14147, U.S. Pat. No. 5,698,662. In this poly(propylene imine) dendrimer series, there is no heteroatom or linker functionalities between the branch points, that are constituted by tertiary amines. The branch points are separated typically by alkylene units. Other popular dendrimers studied extensively, are by Fréchet and co-workers, J. Am. Chem. Soc. 7638 (1990); Majoral and co-workers, Science, 1981 (1997) and Fréchet and co-workers U.S. Pat. No. 5,041,516. Low molecular weight poly (propyl ether imine) dendritic molecules with ether linkages and imine branch points wherein the molecular weight is less than 3600 g/mol, with ester units at the surfaces has been described in, Rama Krishna and Jayaraman, J. Org. Chem. 2003, 9694. Although four and higher generation dendrimers were highly desired as the same has more versatility than an third and lower generation dendrimers, it was found that fourth and higher generation dendrimers could not be constructed by the protocol that yielded dendrimers up to three generations.
Each dendrimer is characterized by its unique constitution and thus attendant physico-chemical and biological properties differ significantly. Although there exists a number of dendrimers, the ones that have been utilized in a wide range of studies remain limited. The poly(amido amine) and poly(propylene imine) dendrimers are the most studied dendritic macromolecules, in general. Due to the physico-chemical properties that reside with the molecular constitution of the dendrimers, identification of new monomers and synthesis of new dendrimers are important target areas in the branch of polymer/macromolecular science and technology. It is also necessary to achieve higher and higher generational dendrimers as each such higher generation dendrimer improves the scope of application of such dendrimers. A large number of technologically important utilities such as those in power, energy, healthcare, medical, engineering, consumer goods, environmental, electronics and optoelectronics are expected to benefit by the unique architectural characteristics of the dendritic macromolecules.